The production of high quality articles, particularly photographic, photothermographic, and thermographic articles, consists of applying a thin film of a coating solution onto a continuously moving substrate preferably a continuous web. Thin films can be applied using a variety of techniques including: dip coating, forward and reverse roll coating, wire wound rod coating, blade coating, slot coating, slide coating, and curtain coating. Coatings can be applied as a single layer or as two or more superimposed layers. Although it is most convenient for the substrate to be in the form of a continuous web, it may also be formed of a succession of discrete sheets.
When a web material is continuously fed from a plurality of successive rolls, the ends of the rolls may be spliced together to eliminate interruption to the web feed. Different types of splices can be formed, including a lap splice, a butt splice, and a gap splice. A lap splice is formed when a portion of an expiring web overlies a portion of a web from a new roll with the under surface of the overlapped portion of one of the webs adhering to the upper surface of the other web. With a butt splice, the trailing end of the expiring web is in intimate contact with the leading end of the new web, but no overlap exists. A gap splice is formed when no overlap exists and the ends of the expiring web and new web are separated. For the butt splice and the gap splice, tape may be employed to connect the ends. U.S. Pat. No. 5,277,731 relates to the formation of a butt splice. U.S. Pat. Nos. 4,652,329 and 5,045,134 teach apparatus and methods for forming a splice and are hereby incorporated by reference in their entireties.
The coating gap between the moving web and the coating die is typically less than about 4 millimeters (0.157 inch). Web splices, debris on, or defects in, the web in excess of the coating gap can cause serious damage to the coating die. It is common practice to retract the coating die, and break the coating bead, to permit web splices to pass through the coating gap. After the web splice passes the coating gap, the pick-up cycle must be repeated to reestablish the coating bead.
There are two important capabilities required of machines used to apply the coating solution to a continuous web or a series of discrete sheets. One is the ability to adjust the initial coating gap accurately often measured in microns. Second, is the ability to detect web splices, debris on, or defects in the web where the coating die is momentarily retracted to avoid damage and immediately returned to the exact previous position to resume the coating operation.
Numerous mechanisms and procedures have been proposed to implement one or the other of these two capabilities, as indicated in the following references.
U.S. Pat. No. 4,522,678 discloses that in the manufacture of film containing integral fasteners and the like, the film commonly exits through an elongated slot die while profiles for the fasteners exit through a smaller configured slot located laterally along the film die slot. The fastener profiles normally carry a thickened base so that the profiles will stand without undue tipping for better interengagement with one another. It has been found that it is advantageous if the base of the profile can be adjusted transversely of the film slot so that the size of the base can be adjusted on-line. The '678 patent allows the die block to be transversely adjustable by a combination of a U-shaped mounting block, an inverted T-shaped profile plate and an eccentric adjustment pin, assembled in a fashion so that the eccentric pin can be rotated to adjust transversely the gap through which the profile base passes just before joining the film. This device also makes possible measurement of the gap for the profile base indirectly on line.
U.S. Pat. No. 4,808,444 discloses a coating method and apparatus in which a coating composition is applied from a hopper to a web continuously travelling on a backing roller. The backing roller is rapidly moved by a pneumatic mechanism relative to the hopper between positions at which the composition can and cannot be applied to the travelling web in order to avoid thick coating at a leading portion or at a spliced portion of the web.
U.S. Pat. No. 5,154,951 discloses an apparatus and method for bead coating a web with liquid composition with a pressure differential applied across the bead of composition between the lip of the slide hopper and the web. An enclosure is disposed under and open to the bead. Vacuum is applied to the enclosure by a turbine driven by an AC induction motor. Servo means are provided for regulating the speed of the motor and thereby the pressure differential across the bead. The AC motor and the servo means allow the desired pressure to be maintained without surges and allows the differential pressure to be rapidly changed, as for the passage of a splice in the web through the bead.
U.S. Pat. No. 5,626,888 discloses a flat-sheet die for an extrusion system for producing flat sheets has an extremely close succession of actuators, by way of which at least one die lip is adjustable with a narrow-band bending line in order to define the outlet gap.
U.S. Pat. No. 5,853,482 discloses an apparatus and method for applying a coating solution to a running substrate using a slot die having two die lips forming a gap therebetween. The gap also defines an outlet for releasing the coating solution to the substrate. The lips have plurality of manifold chambers communicating with gas feeder and coating solution feeder provided in the die lips. The manifold chambers communicate with the outlet. The width of the coating solution is adjustable with the gas pressure applied to the gas feeder.
U.S. Pat. No. 5,953,953 discloses an apparatus and method for detecting the presence of a splice in a running length of web material, particularly photosensitive web material. The apparatus includes first and second encoders coupled to first and second rollers, respectively. As the web material is transported across the rollers, the speeds of the rollers are continuously and simultaneously detected. The rollers will travel at substantially the same speed when the web is being transported across both rollers. The presence of the splice is detected when the speeds of the two rollers differ.
U.S. Pat. No. 6,576,296 discloses a method and apparatus for continuously coating moving web and splices with a coating fluid. The system includes a slide coating die having a slide surface with at least one feed slot for extruding the coating fluid onto the moving web. The slide coating die defines a coating gap with the moving web. The coating gap is adjustable between a coating position and a splice coating position. A web guide is positioned to guide the moving web in a first direction past the slide coating die such that a coating bead of the coating fluid can be formed in the coating gap. A vacuum system is positioned to generate a reduced pressure condition along a lower surface of the slide coating die. The vacuum system defines a vacuum gap with the moving web. The vacuum gap is adjustable independent of the coating gap between a coating position and a splice coating position. A detector signals an increase in web thickness. A controller is functionally connected to the detector. The controller adjusts the coating gap and the vacuum gap to the splice coating position in response to an increase in web thickness in excess of a predetermined magnitude while maintaining a stable coating bead.
U.S. Pat. No. 6,688,580 discloses a die for dispensing a fluid onto a substrate, wherein the die has an movable lip adjacent a fixed lip to form a die opening therebetween. An actuator is mechanically connected to the movable lip and is operable to automatically move the movable lip with respect to the fixed lip in association with a fluid dispensing process, thereby changing a volume of the die opening. The adjustable die is often a slot die and is used with a fluid dispensing valve having an upstream valve ball. The actuator can be an electromechanical actuator such as a piezoelectric actuator or a fluid operated actuator.
U.S. Pat. No. 6,706,315 discloses a process that includes: providing a moving substrate; applying at least one coating layer wherein the at least one coating is a photoconductive material, an electrically insulating material, a hole transport material, an anti-curl material, or an adhesive material onto the moving substrate with a slot die coater equipped with at least one position sensor mounted on at least one end of the slot die coater, and for example, applying from one to about five coating layers on the substrate; sensing the position of the slot die coater relative to the moving substrate with at least one position sensor; and, when the position of the slot die coater relative to the moving substrate deviates from a set of predetermined coordinates, iteratively adjusting the position of the die coater relative to the surface of the substrate to return to the set of predetermined coordinates.
U.S. Publication No. 2003/0080307 discloses a die for dispensing a fluid onto a substrate, wherein the die has a movable lip adjacent a fixed lip to form a die opening therebetween. An actuator is mechanically connected to the movable lip and is operable to automatically move the movable lip with respect to the fixed lip in association with a fluid dispensing process, thereby changing a volume of the die opening. The adjustable die is often a slot die and is used with a fluid dispensing valve having an upstream valve ball. The actuator can be an electromechanical actuator such as a piezoelectric actuator or a fluid operated actuator.
U.S. Publication No. 2003/0157243, U.S. Publication No. 2003/0054107 and U.S. Pat. No. 6,863,730 disclose an apparatus including: a movement device that moves an object to be coated; a slot die coater equipped with a position sensor mounted on at least one end of the slot die coater and which slot die coater controllably dispenses coating material onto the moving object; and at least one servo motor-controller system in electrical contact with the position sensor, wherein the position sensor senses the position of the slot die coater relative to the object and wherein the at least one servo motor-controller system adjusts the position of the slot die coater relative to the object if the position of the slot die coater relative to the moving substrate deviates from a set of predetermined coordinates.
None of the prior references disclose the ability to simultaneously achieve high accuracy coating gap setup and ability to retract and reposition the slot die with high precision. Likewise, none of the prior references disclose the ability to detect the difference between a substrate splice and a coating defect to subsequently position the slot die at different distances from the substrate to minimize the potential for slot die damage. Furthermore, none of the prior references disclose the use of feed-forward controllers which have the capability to minimize the amount of off-specification coated product.